Tech Tools Reveal Terroir

Geographic Information System helps define B.C. grape quality

by
Pat Bowen

HIGHLIGHTS

The Pacific Agri-Food Research Centre took a modern approach in evaluating vineyard sites by focusing on grape quality and using geographic information system (GIS) and statistical tools to reveal the most influential components of terroir.

Varietal blocks first were mapped with GPS and became the basic units for data collection. Information from more than 2,500 variety blocks was collected in a database, organized in three modules: Site Conditions, Cultural Management and Vineyard Performance.

Results included: an assessment of varietal suitability by soil and climate; effects of yield and fruit maturity on quality and relation of measurable flavor and aroma components (norisoprenoids) to environmental conditions and management practices.

Six years ago we embarked on an industry-wide study to determine the combinations of vineyard site conditions, varieties and management practices that lead to superior quality winegrapes in the Okanagan and Similkameen valleys. Ten years prior, the industry had transformed itself from a producer of mostly bulk wine based on French hybrids, to a highly reputed producer of V.vinifera varietal wines. During the hybrid era, government specialists published an atlas showing the grapegrowing suitability of soils and climate in the region. Although geared toward hybrids and high yields, the atlas became a key resource for selecting vinifera production sites and varieties. Our goal was to take a modern approach in evaluating vineyard sites by focusing on vinifera quality and using geographic information system (GIS) and statistical tools to reveal the most influential components of terroir.

Initial work began with the collection of vineyard block perimeter coordinates by GPS. Ninety-eight percent of the grapegrowers in the Okanagan and Similkameen valleys agreed to have their vineyards mapped and to contribute data to our GIS research. Locating the block boundaries was critical for assessing underlying geographic features and for determining the acreage of varieties planted in each region. Vineyard maps, created by overlaying varietal blocks on elevation contours, roadways and water features, were provided to growers and include accurate measures of block areas. We used a combination of ESRI ArcGIS software to build the maps and Microsoft Access to build our relational database. Our GPS system is a Trimble GeoExplorer 3 with Pathfinder software.

Varietal blocks were the basic units for data collection. Information from more than 2,500 varietal blocks is in the database, organized in three modules: Site Conditions, Cultural Management and Vineyard Performance.

The site conditions module includes soil, topographic and climatic characteristics. Working with soil scientist Scott Smith, soils were identified by first overlaying the block boundaries on soil survey maps. A soil specialist then visited each vineyard, verified the soil series, adjusted the location of soil boundaries and collected additional data on soil properties, block topography and surrounding landforms. Soil maps were provided to growers with detailed descriptions of the soils identified.

Grapegrowers in the Okanagan and Similkameen valleys had their vineyards mapped and contributed data to a study evaluating individual vineyard sites for their suitability to grow vinifera grapes.

Climate was characterized using data from government and grower weather stations. In individual vineyards, mesh networks of sensor-loggers were used to study fine-grained climatic variation, either as snapshot views in real-time--such as to observe the formation of frost pockets--or as average or cumulative views of features such as growing degree-days, to assist in selecting zones for precision management.

Data in the cultural management and vineyard performance modules were gathered by surveying and inteviewing growers and winemakers. The fruit and wine quality data include chemical composition, quality ratings from winemakers, vineyard sources of medal-winning wines and wine sensory descriptions.

Some of our first data analyses addressed long-standing questions in viticulture: What is the relationship between fruit yield and quality, and how does fruit maturity influence quality? Analysis of the yield-quality relationship verified that fruit quality, as rated by winemakers, suffers at high yields. Merlot and Chardonnay crops exceeding 5 tons per acre were never rated excellent, but vineyards yielding less than 3 tons/acre were rated from poor to excellent. In other words, overcropping reduces quality, but low production does not assure quality.

The relationship between fruit maturity and quality is a hot topic, as growers and winemakers are hearing the hype that prolonging the hang time of red varieties to extend their maturation produces the most desirable wines. Most growers in B.C. strive to maximize fruit quality, and time harvests for when flavors are optimal, but for some growers the temptation remains to push yields and produce fruit that has achieved only acceptable target soluble solids (Brix) and acid levels.

Our data revealed only weak relationships between fruit quality and maturity as indicated by soluble solids. For white varieties such as Chardonnay, not surprisingly all fruit rated as excellent had soluble solids between 23º and 25º Brix. For Merlot, excellence was achieved between 24º and 27º Brix. Even so, some fruit harvested within those maturity ranges was rated as only fair or poor in quality. Clearly, getting fruit mature should not be the singular goal of viticulture.

Using our GIS tools, we assessed varietal suitability by first partitioning the production area into growing regions based on soil and climate. The six regions defined include the Similkameen Valley and five regions in the Okanagan Valley from the U.S. border to near the city of Vernon, 100 miles to the north (see map). The regions range in annual cumulative growing degree-days from ca. 2,100 to 2,700. Dominant soil textures range from loamy sands to silt and clay loams. Acreage of varieties planted varied widely among the regions, and was taken into account in the suitability assessments.

To gauge quality, we used results from an annual wine competition in which numerous wines of each variety and region were assessed by blind judging. For the eight most widely planted varieties, clear differences in suitability to regions were found. Merlot and Cabernet Sauvignon are best suited to the warmest, southern-most region, Black Sage-Osoyoos. Pinot Noir excels in Kelowna, the coolest region. Chardonnay performs better in the northern regions, Kelowna and Penticton, whereas Pinot Blanc is better suited to Black Sage-Osoyoos. Riesling and Gewürztraminer are favored from Vaseaux-Oliver, where vineyards are planted on higher-elevation sites. Pinot Gris performs exceptionally in the Similkameen Valley, but also excels in the Penticton region, on the lakeside terrace known as the Naramata Bench.

The Naramata Bench, a lakeside terrace near Penticton, was shown to be an outstanding location for growing Pinot Gris.Courtesy Mission Hill Family Estate

Flavor and aroma compounds can be influenced during berry development by subtle differences in environmental conditions and management practices. In Chardonnay, these include minute levels of norisoprenoids that impart the floral and fruity aromas in Chardonnay wines. In a study with colleagues Benoit Girard, Kevin Usher and Nigel Eggers, norisoprenoids were analyzed in Chardonnay fruit collected over three years from 40 vineyards covering all regions. Relations of norisoprenoid levels with climate and cultural management indicated that fruit temperature is critical to norisoprenoid synthesis. Excessive leaf removal, which exposed clusters, reduced norisoprenoid levels, and higher levels were found in 2001 and 2002 than in 2003, which had a hotter summer. Vineyards with a western aspect and rows oriented north-south produced fruit with the highest norisoprenoid levels.

Working with sensory researchers Margaret Cliff and Marjorie King, we are currently exploring terroir influences on Merlot wines. Several nonblended wines originating from each of the six growing regions were evaluated blindly by a trained 31-judge panel. The judges clearly discriminated regional differences among the wines based on their flavor and aroma profiles. Also distinguished were differences among winery styles. These findings surprised us, not because they conflicted with our expectations but because the data so clearly confirmed our notions of terroir. Wine character was shown to be influenced by vineyard site conditions, but winemaking techniques affected and added style to the wines.

It seems that in all of our GIS research, the rigor of scientific data gathering and analysis simply reconfirmed what our experience and intuition had already told us: Great wines come from combining site selection with appropriate viticulture and winemaking skill and style.

(Pat Bowen is a research scientist at the Pacific Agri-Food Research Centre in Summerland, B.C. Further details of the construction and analysis of the Okanagan/Similkameen Viticulture GIS are reported in Geoscience Canada 32:161-176. To comment on this article, e-mail edit@winesandvines.com.)